Page 1
Recibido 13 de mayo 2020 Aceptado 18 de septiembre 2020
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 pp 754 - 772 ISSN 1683-0768
Development of shape stabilized thermal energy storage materials based on inorganic chloride salts
by direct sol-gel method
Desarrollo de materiales de almacenamiento de energiacutea teacutermica estabilizados en forma basados en sales de cloruro inorgaacutenico
mediante el meacutetodo directo sol-gel
Yanio E Miliaacuten Svetlana Ushak
Center for Advanced Research in Lithium and Industrial Minerals (CELiMIN) Universidad de Antofagasta y Departamento de Ingniera Quiacutemica y Procesos de Minerales de Universidad de Antofagasta Avenue Universidad de Antofagasta
02800 Antofagasta Chile
svetlanaushakuantofcl
Abstract The potential of several improved materials was analyzed for thermal energy storage in this work specifically for latent heat storage (LHS) and for thermochemical energy storage (TCS) The use of a direct sol-gel process using tetraethyl orthosilicate as monomer was applied to obtain shape stabilized ndash thermal energy storage materials (SS-TES material) based on different inorganic salts (MgCl26H2O MnCl2 and LiCl) and wastes from non-metallic mining industry bischofite (95 of MgCl26H2O) and carnallite (73 of KClMgCl26H2O) A detailed analysis was offered for the developed materials based on x-ray diffraction scanning electronic microscopy and thermal analyses A new low-cost material of carnalliteSiO2 showed an atypical absorption peak at 50 degC which increase with the content of carnallite in the final material indicating a possible potential as a thermochemical storage medium for low temperature applications below 100 degC However the application of the sol-gel method under the conditions studied in this work did not allow to obtain SS-TES materials based on MgCl26H2O MnCl2 and carnallite for LHS which indicates that future adjustments are necessary to obtain satisfactory results
Keywords shape stabilized thermal energy storage materials bischofite carnallite sol-gel tetraethyl orthosilicate silicon dioxide
Resumen En este trabajo se analizoacute el potencial de varios materiales mejorados para el almacenamiento de energiacutea teacutermica especiacuteficamente para el almacenamiento de calor latente (LHS) y para el almacenamiento de energiacutea termoquiacutemica (TCS) Se aplicoacute el uso de un proceso directo sol-gel utilizando tetraetil ortosilicato como monoacutemero para obtener materiales de almacenamiento de energiacutea teacutermica estabilizada de forma (material SS-TES) a base de diferentes sales inorgaacutenicas (MgCl26H2O MnCl2 y LiCl) y residuos de Industria minera no metaacutelica bischofita (95 de MgCl26H2O) y carnalita (73 de KClMgCl26H2O)
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 755
Se ofrecioacute un anaacutelisis detallado de los materiales desarrollados basado en difraccioacuten de rayos X microscopiacutea electroacutenica de barrido y anaacutelisis teacutermicos Un nuevo material de bajo costo de carnalita SiO2 mostroacute un pico de absorcioacuten atiacutepico a 50 deg C que aumenta con el contenido de carnalita en el material final lo que indica un posible potencial como medio de almacenamiento termoquiacutemico para aplicaciones de baja temperatura por debajo de 100 deg C Sin embargo la aplicacioacuten del meacutetodo sol-gel en las condiciones estudiadas en este trabajo no permitioacute obtener materiales SS-TES a base de MgCl26H2O MnCl2 y carnalita para LHS lo que indica que son necesarios ajustes futuros para obtener resultados satisfactorios
Palabras clave materiales de almacenamiento de energiacutea teacutermica estabilizados en forma bischofita carnalita sol-gel ortosilicato de tetraetilo dioacutexido de silicio
1 Introduction
The solar energy technologies can be combined with thermal energy storage
(TES) systems which can be classified as thermochemical heat (TCS) sensible heat
(SHS) and latent heat (LHS) storage [1] The search of potential materials for TES
systems and the optimization of their thermal performance are still a challenge The
availability and low-cost of these TES materials are important factors to consider for
the sustainable development of any kind of solar based storage system [2] Inorganic
materials including salt hydrates metals and alloys are recently investigated for TES
since have high thermal conductivity energy storage densities high working
temperature range and low-cost [3] Moreover various inorganic wastes and by-
products from non-metallic mining industry are available without any application
accumulating in mining lands and constituting a serious risk to the environment In
recent years the potentiality of these materials for TES applications has increased
due to its cost being close to zero [4 5] Some of these wastes were proposed for
SHS like astrakanite (Na2SO4middotMgSO4middot4H2O) [6] kainite (KClmiddotMgSO4middot3H2O) [6] and
NaCl [7] as by-products from the obtained processes of nonmetallic mining industry
Among the materials displaying potential as thermochemical material for TCS can be
mentioned astrakanite and potassium carnallite (KClMgCl26H2O) which exhibited
release of water below 300 degC [59] Similarly the dehydration reaction of bischofite
[10] and carnallite [11] were analyzed as low-cost TCS materials Compounds
employed for LHS and called as phase change materials (PCMs) had been studied in
several works including those from inorganic wastes [5-13] A dehydrated product
obtained from astrakanite showed potential to be applied as PCM at high
temperature (550 degC ndash 750 degC) [56] Bischofite with a phase change point at 100 degC
and a latent heat (ΔH) around 115 kJ kg-1 was identified as a potential PCM with
similar thermophysical characteristics to synthetic magnesium chloride hexahydrate
besides with a lower cost [12] In fact the successful application of bischofite
impregnated in expanded graphite (EG) was demonstrated for thermal regulation on
756middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
lithium batteries absorbing the produced heat from batteries and therefore
extending battery life and enhancing their performance [13] However all these
inorganic materials present some adverse effects as subcooling (around 35 degC) and
phase segregation [1214] which reduce the usefulness of the materials and in some
cases could prevent entirely the heat recovery from the material
Among the methods used to reduce the degree of subcooling are the addition
of nucleating agents mechanical agitation chemical modifications and the
encapsulation of the PCMs among others [14-16] In a consecutive work bischofite
subcooling degree was reduced to 234 degC by the formulation of an inorganic eutectic
mixture based on 40 wt bischofite and 60 wt Mg(NO3)2middot6H2O with a melting
point (Tm) of 582 degC and Δh around 1170 kJ kg-1 [16] Nevertheless lower
subcooling degrees need to be achieved for real applications
Encapsulation methods are among the most used techniques to improve thermal
properties of inorganic TES materials and can be performed in two different ways
core-shell encapsulation and shape-stabilized thermal energy storage materials (SS-
TES materials) [14 15] Only few works related to the encapsulation of non-metallic
industrial wastes and by-products [1819] are available Bischofite was micro-
encapsulated by a fluidized bed method using acrylic acid as polymer and chloroform
as solvent after compatibility studies of several solvents and several polymers The
final microcapsules had excellent melting temperatures and latent heat (1046 degC and
95 kJkg-1 respectively) resulting in a decrease in subcooling degree and avoiding
leakage of the hydrate when it melts [18] MgCl2middot6H2O-Mg(NO3)2middot6H2Ofumed
silica composites was obtained as SS-TES material by impregnation method basically
mixing the eutectic salts with dried fumed silica (85 degC 2 h) Thermal conductivity
thermal stability and cycle stability were improved for the final material compared
with the eutectic salt [19] However the SS-TES materials currently developed are
still insufficient to meet the demand and the requirements for practical and tangible
applications The search for economic options of support materials with a practical
thermal performance and an effective-simple method to obtain SS-TES materials are
still required Support materials (SMs) based on silicon dioxide were used successfully
to obtain SS-TES materials since they are characterized for the presence of pores
and a large internal surface area [20-22] A one-step direct sol-gel technique was
employed to develop lithium salts (LiCl and LiNO3) based shape stabilized phase
change materials (SS-PCMs) with tetraethyl orthosilicate (TEOS) improving cycling
stability and sub-cooling related with the pure salts [23] As well a Na2SO4 based SS-
PCM was developed by the same technique and the influence of pH (acid and basic
hydrolysis) and PCM content were also analyzed [24] Henceforward the main
objective of this work was to develop new TES materials with stabilized shape based
on inorganic salts (MgCl2middot6H2O MnCl2 and LiCl) and low-cost wastes from non-
metallic mining industry (bischofite and carnallite) by the sol-gel technique
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 757
previously developed with TEOS as monomer and via acid hydrolysis Thus the
influence of the chemical nature of the inorganic TES material was evaluated The
potential of the developed materials was analyzed for LHS and TCS
2 Materials and Procedures
21 Materials
Tetraethyl orthosilicate TEOS (reactant grade Sigma-Aldrich China) and
ethanol (absolute grade for analysis Merck Ka) were employed in the synthesis of
SiO2 materials as SMs The syntheses were produced by acid hydrolysis using
hydrochloric acid (37 ) of analysis grade obtained from Merck KGaA Germany
Magnesium chloride hexahydrate MgCl26H2O manganese chloride MnCl2 and
lithium chloride LiCl as reference material (all grade salts for analysis) were obtained
from Merck KGaA Germany Carnallite and bischofite were provided by the
Rockwood Lithium mining company Antofagasta Chile Distilled water was
obtained in the laboratory using a water deionizing system SIMS600CP MIlipore
Simplicity Personal Ultrapure Water System
22 Experimental procedure
The used sol-gel procedure was based on the method proposed by Milian et al
[23 24] via acid hydrolysis of the monomers to initiate the polymerization reaction
Briefly tetraethyl orthosilicate was mixed with the same amount of ethanol under
continuous stirring HCl (30 ) and distilled water were added and this solution was
continuously stirred over two hours to produce the -Si-O-Si- pre-polymer This pre-
polymeric solution was employed straight to develop the SS-TES materials The
selected inorganic materials (Table 1) previously dissolved in deionized water were
mixed with the prepolymer and then stored for 10 days Once the SS-TES materials
were achieved in solid phase materials were dried in an oven at 60 degC and finally
mechanically pulverized In this way sol-gel procedure was employed to obtain SS-
TES materials based on wastes from non-metallic mining industry bischofite
(MgCl2middot6H2O) and carnallite (KMgCl3middot6H2O) Eight new stabilized materials based
on bischofite and carnallite with different inorganic salt contents (Table 1) were
prepared
758middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
Table 1 Experimental conditions of cyclic stability studies for inorganic SS-
TES materials
Inorganic SS-TES materials
TES material content (wt )
Number of cycles
Temperature range (degC)
Coolingheating rate
LiCl 50 5 550 ndash 750
10 degC min-1
MgCl26H2O 50 2 30 ndash 150
MnCl2 50 2 25 ndash 200
Bischofite 20 30 40 and 60
2 25 ndash 150
Carnallite 20 30 40 and 60
2 25 ndash 150
23 SEM-EDX and XRD characterization of the SS-TES materials
The characterization of the new materials was performed by a Scanning Electron
Microscopy (SEM) with Energy Dispersion X-ray Spectroscopy (EDS) with a Jeol
machine Model JSM6360 LV a Siemens X-ray diffractometer (automatic and
computerized D5000 model) equipped with a scintillation detector and the
DiffracPlus software for X-ray diffraction (XRD) analysis
24 Thermal and cycling tests of the SS-TES materials
Thermal stability was studied using a thermogravimetry equipment (TG)
coupled with differential scanning calorimeter (DSC) (Mettler Toledo Model 1 1100
LF) from 100 to 350 degC with a heating cooling rate of 10 degC min-1 using around
10 mg of the sample and alumina crucible with lid Thermal properties like melting
temperature (Tm) and latent heat (ΔH) and cyclic stability of the obtained SS-PCM
were determined by a DSC 204 F1 Phoenix NETZSCH under a pure nitrogen
atmosphere with constant gas volumetric flow of 20 mL min-1 Cyclic stability was
determined by the DSC 204 F1 Phoenix NETZSCH using different temperature
ranges and cycle numbers for each sample (Table 1) to estabish the opportunities
of the developed SS-TES materials for LHS The same experiments specifically the
thermal dehydration processes of the hydrates were used to analyze the TCS
potentiality of the materials
3 Results and Discussion
Previously a sol-gel technique was developed to obtain SS-PCMs based on Li
salts [23] Now in this work the previously developed method was applied to obtain
SS-TES materials employing firstly inorganic salts and then wastes from the non-
metallic mining industry such as bischofite and carnallite The obtained SS-TES
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 759
materials were engaged not only for LHS but also for their potentiality as TCS
materials
31 Development of SS-TES materials employing commercial inorganic compounds
311 SEM-EDX and XRD characterization of SS-TES materials
Firstly 50 wt MgCl2middot6H2O and 50 wt MnCl2 were prepared by the
described method as two new SS-TES materials In addition a 50 wt LiCl based
material was also synthetized as a reference material of the sol-gel procedure
according to a previous publication [23] and to compare with new magnesium and
manganese based materials at the same salt content The SEM images obtained for
the MgCl2 based SS-TES material showed separated phases the SiO2 support
material with the saltand segregated salt particles which present an irregular
morphology and a flat surface respectively (Fig 1 a b and c) Smooth surface
particles were obtained for the MnCl2 stabilized material and the formation of
detached salt particles from the stabilized material was also observed (Fig 1 d e and
f) Conversely the LiCl salt was found covering the entire surface of the polymer as
well as forming part of the same solid phase of these particles (Fig 1 g h and I) as
was previously observed by Milian et al [23] The obtainment of separated phases by
this sol-gel technique was associated with a high weight percentage (wt) of the
TES material on the synthesis [23 24]
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 2
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 755
Se ofrecioacute un anaacutelisis detallado de los materiales desarrollados basado en difraccioacuten de rayos X microscopiacutea electroacutenica de barrido y anaacutelisis teacutermicos Un nuevo material de bajo costo de carnalita SiO2 mostroacute un pico de absorcioacuten atiacutepico a 50 deg C que aumenta con el contenido de carnalita en el material final lo que indica un posible potencial como medio de almacenamiento termoquiacutemico para aplicaciones de baja temperatura por debajo de 100 deg C Sin embargo la aplicacioacuten del meacutetodo sol-gel en las condiciones estudiadas en este trabajo no permitioacute obtener materiales SS-TES a base de MgCl26H2O MnCl2 y carnalita para LHS lo que indica que son necesarios ajustes futuros para obtener resultados satisfactorios
Palabras clave materiales de almacenamiento de energiacutea teacutermica estabilizados en forma bischofita carnalita sol-gel ortosilicato de tetraetilo dioacutexido de silicio
1 Introduction
The solar energy technologies can be combined with thermal energy storage
(TES) systems which can be classified as thermochemical heat (TCS) sensible heat
(SHS) and latent heat (LHS) storage [1] The search of potential materials for TES
systems and the optimization of their thermal performance are still a challenge The
availability and low-cost of these TES materials are important factors to consider for
the sustainable development of any kind of solar based storage system [2] Inorganic
materials including salt hydrates metals and alloys are recently investigated for TES
since have high thermal conductivity energy storage densities high working
temperature range and low-cost [3] Moreover various inorganic wastes and by-
products from non-metallic mining industry are available without any application
accumulating in mining lands and constituting a serious risk to the environment In
recent years the potentiality of these materials for TES applications has increased
due to its cost being close to zero [4 5] Some of these wastes were proposed for
SHS like astrakanite (Na2SO4middotMgSO4middot4H2O) [6] kainite (KClmiddotMgSO4middot3H2O) [6] and
NaCl [7] as by-products from the obtained processes of nonmetallic mining industry
Among the materials displaying potential as thermochemical material for TCS can be
mentioned astrakanite and potassium carnallite (KClMgCl26H2O) which exhibited
release of water below 300 degC [59] Similarly the dehydration reaction of bischofite
[10] and carnallite [11] were analyzed as low-cost TCS materials Compounds
employed for LHS and called as phase change materials (PCMs) had been studied in
several works including those from inorganic wastes [5-13] A dehydrated product
obtained from astrakanite showed potential to be applied as PCM at high
temperature (550 degC ndash 750 degC) [56] Bischofite with a phase change point at 100 degC
and a latent heat (ΔH) around 115 kJ kg-1 was identified as a potential PCM with
similar thermophysical characteristics to synthetic magnesium chloride hexahydrate
besides with a lower cost [12] In fact the successful application of bischofite
impregnated in expanded graphite (EG) was demonstrated for thermal regulation on
756middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
lithium batteries absorbing the produced heat from batteries and therefore
extending battery life and enhancing their performance [13] However all these
inorganic materials present some adverse effects as subcooling (around 35 degC) and
phase segregation [1214] which reduce the usefulness of the materials and in some
cases could prevent entirely the heat recovery from the material
Among the methods used to reduce the degree of subcooling are the addition
of nucleating agents mechanical agitation chemical modifications and the
encapsulation of the PCMs among others [14-16] In a consecutive work bischofite
subcooling degree was reduced to 234 degC by the formulation of an inorganic eutectic
mixture based on 40 wt bischofite and 60 wt Mg(NO3)2middot6H2O with a melting
point (Tm) of 582 degC and Δh around 1170 kJ kg-1 [16] Nevertheless lower
subcooling degrees need to be achieved for real applications
Encapsulation methods are among the most used techniques to improve thermal
properties of inorganic TES materials and can be performed in two different ways
core-shell encapsulation and shape-stabilized thermal energy storage materials (SS-
TES materials) [14 15] Only few works related to the encapsulation of non-metallic
industrial wastes and by-products [1819] are available Bischofite was micro-
encapsulated by a fluidized bed method using acrylic acid as polymer and chloroform
as solvent after compatibility studies of several solvents and several polymers The
final microcapsules had excellent melting temperatures and latent heat (1046 degC and
95 kJkg-1 respectively) resulting in a decrease in subcooling degree and avoiding
leakage of the hydrate when it melts [18] MgCl2middot6H2O-Mg(NO3)2middot6H2Ofumed
silica composites was obtained as SS-TES material by impregnation method basically
mixing the eutectic salts with dried fumed silica (85 degC 2 h) Thermal conductivity
thermal stability and cycle stability were improved for the final material compared
with the eutectic salt [19] However the SS-TES materials currently developed are
still insufficient to meet the demand and the requirements for practical and tangible
applications The search for economic options of support materials with a practical
thermal performance and an effective-simple method to obtain SS-TES materials are
still required Support materials (SMs) based on silicon dioxide were used successfully
to obtain SS-TES materials since they are characterized for the presence of pores
and a large internal surface area [20-22] A one-step direct sol-gel technique was
employed to develop lithium salts (LiCl and LiNO3) based shape stabilized phase
change materials (SS-PCMs) with tetraethyl orthosilicate (TEOS) improving cycling
stability and sub-cooling related with the pure salts [23] As well a Na2SO4 based SS-
PCM was developed by the same technique and the influence of pH (acid and basic
hydrolysis) and PCM content were also analyzed [24] Henceforward the main
objective of this work was to develop new TES materials with stabilized shape based
on inorganic salts (MgCl2middot6H2O MnCl2 and LiCl) and low-cost wastes from non-
metallic mining industry (bischofite and carnallite) by the sol-gel technique
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 757
previously developed with TEOS as monomer and via acid hydrolysis Thus the
influence of the chemical nature of the inorganic TES material was evaluated The
potential of the developed materials was analyzed for LHS and TCS
2 Materials and Procedures
21 Materials
Tetraethyl orthosilicate TEOS (reactant grade Sigma-Aldrich China) and
ethanol (absolute grade for analysis Merck Ka) were employed in the synthesis of
SiO2 materials as SMs The syntheses were produced by acid hydrolysis using
hydrochloric acid (37 ) of analysis grade obtained from Merck KGaA Germany
Magnesium chloride hexahydrate MgCl26H2O manganese chloride MnCl2 and
lithium chloride LiCl as reference material (all grade salts for analysis) were obtained
from Merck KGaA Germany Carnallite and bischofite were provided by the
Rockwood Lithium mining company Antofagasta Chile Distilled water was
obtained in the laboratory using a water deionizing system SIMS600CP MIlipore
Simplicity Personal Ultrapure Water System
22 Experimental procedure
The used sol-gel procedure was based on the method proposed by Milian et al
[23 24] via acid hydrolysis of the monomers to initiate the polymerization reaction
Briefly tetraethyl orthosilicate was mixed with the same amount of ethanol under
continuous stirring HCl (30 ) and distilled water were added and this solution was
continuously stirred over two hours to produce the -Si-O-Si- pre-polymer This pre-
polymeric solution was employed straight to develop the SS-TES materials The
selected inorganic materials (Table 1) previously dissolved in deionized water were
mixed with the prepolymer and then stored for 10 days Once the SS-TES materials
were achieved in solid phase materials were dried in an oven at 60 degC and finally
mechanically pulverized In this way sol-gel procedure was employed to obtain SS-
TES materials based on wastes from non-metallic mining industry bischofite
(MgCl2middot6H2O) and carnallite (KMgCl3middot6H2O) Eight new stabilized materials based
on bischofite and carnallite with different inorganic salt contents (Table 1) were
prepared
758middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
Table 1 Experimental conditions of cyclic stability studies for inorganic SS-
TES materials
Inorganic SS-TES materials
TES material content (wt )
Number of cycles
Temperature range (degC)
Coolingheating rate
LiCl 50 5 550 ndash 750
10 degC min-1
MgCl26H2O 50 2 30 ndash 150
MnCl2 50 2 25 ndash 200
Bischofite 20 30 40 and 60
2 25 ndash 150
Carnallite 20 30 40 and 60
2 25 ndash 150
23 SEM-EDX and XRD characterization of the SS-TES materials
The characterization of the new materials was performed by a Scanning Electron
Microscopy (SEM) with Energy Dispersion X-ray Spectroscopy (EDS) with a Jeol
machine Model JSM6360 LV a Siemens X-ray diffractometer (automatic and
computerized D5000 model) equipped with a scintillation detector and the
DiffracPlus software for X-ray diffraction (XRD) analysis
24 Thermal and cycling tests of the SS-TES materials
Thermal stability was studied using a thermogravimetry equipment (TG)
coupled with differential scanning calorimeter (DSC) (Mettler Toledo Model 1 1100
LF) from 100 to 350 degC with a heating cooling rate of 10 degC min-1 using around
10 mg of the sample and alumina crucible with lid Thermal properties like melting
temperature (Tm) and latent heat (ΔH) and cyclic stability of the obtained SS-PCM
were determined by a DSC 204 F1 Phoenix NETZSCH under a pure nitrogen
atmosphere with constant gas volumetric flow of 20 mL min-1 Cyclic stability was
determined by the DSC 204 F1 Phoenix NETZSCH using different temperature
ranges and cycle numbers for each sample (Table 1) to estabish the opportunities
of the developed SS-TES materials for LHS The same experiments specifically the
thermal dehydration processes of the hydrates were used to analyze the TCS
potentiality of the materials
3 Results and Discussion
Previously a sol-gel technique was developed to obtain SS-PCMs based on Li
salts [23] Now in this work the previously developed method was applied to obtain
SS-TES materials employing firstly inorganic salts and then wastes from the non-
metallic mining industry such as bischofite and carnallite The obtained SS-TES
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 759
materials were engaged not only for LHS but also for their potentiality as TCS
materials
31 Development of SS-TES materials employing commercial inorganic compounds
311 SEM-EDX and XRD characterization of SS-TES materials
Firstly 50 wt MgCl2middot6H2O and 50 wt MnCl2 were prepared by the
described method as two new SS-TES materials In addition a 50 wt LiCl based
material was also synthetized as a reference material of the sol-gel procedure
according to a previous publication [23] and to compare with new magnesium and
manganese based materials at the same salt content The SEM images obtained for
the MgCl2 based SS-TES material showed separated phases the SiO2 support
material with the saltand segregated salt particles which present an irregular
morphology and a flat surface respectively (Fig 1 a b and c) Smooth surface
particles were obtained for the MnCl2 stabilized material and the formation of
detached salt particles from the stabilized material was also observed (Fig 1 d e and
f) Conversely the LiCl salt was found covering the entire surface of the polymer as
well as forming part of the same solid phase of these particles (Fig 1 g h and I) as
was previously observed by Milian et al [23] The obtainment of separated phases by
this sol-gel technique was associated with a high weight percentage (wt) of the
TES material on the synthesis [23 24]
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 3
756middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
lithium batteries absorbing the produced heat from batteries and therefore
extending battery life and enhancing their performance [13] However all these
inorganic materials present some adverse effects as subcooling (around 35 degC) and
phase segregation [1214] which reduce the usefulness of the materials and in some
cases could prevent entirely the heat recovery from the material
Among the methods used to reduce the degree of subcooling are the addition
of nucleating agents mechanical agitation chemical modifications and the
encapsulation of the PCMs among others [14-16] In a consecutive work bischofite
subcooling degree was reduced to 234 degC by the formulation of an inorganic eutectic
mixture based on 40 wt bischofite and 60 wt Mg(NO3)2middot6H2O with a melting
point (Tm) of 582 degC and Δh around 1170 kJ kg-1 [16] Nevertheless lower
subcooling degrees need to be achieved for real applications
Encapsulation methods are among the most used techniques to improve thermal
properties of inorganic TES materials and can be performed in two different ways
core-shell encapsulation and shape-stabilized thermal energy storage materials (SS-
TES materials) [14 15] Only few works related to the encapsulation of non-metallic
industrial wastes and by-products [1819] are available Bischofite was micro-
encapsulated by a fluidized bed method using acrylic acid as polymer and chloroform
as solvent after compatibility studies of several solvents and several polymers The
final microcapsules had excellent melting temperatures and latent heat (1046 degC and
95 kJkg-1 respectively) resulting in a decrease in subcooling degree and avoiding
leakage of the hydrate when it melts [18] MgCl2middot6H2O-Mg(NO3)2middot6H2Ofumed
silica composites was obtained as SS-TES material by impregnation method basically
mixing the eutectic salts with dried fumed silica (85 degC 2 h) Thermal conductivity
thermal stability and cycle stability were improved for the final material compared
with the eutectic salt [19] However the SS-TES materials currently developed are
still insufficient to meet the demand and the requirements for practical and tangible
applications The search for economic options of support materials with a practical
thermal performance and an effective-simple method to obtain SS-TES materials are
still required Support materials (SMs) based on silicon dioxide were used successfully
to obtain SS-TES materials since they are characterized for the presence of pores
and a large internal surface area [20-22] A one-step direct sol-gel technique was
employed to develop lithium salts (LiCl and LiNO3) based shape stabilized phase
change materials (SS-PCMs) with tetraethyl orthosilicate (TEOS) improving cycling
stability and sub-cooling related with the pure salts [23] As well a Na2SO4 based SS-
PCM was developed by the same technique and the influence of pH (acid and basic
hydrolysis) and PCM content were also analyzed [24] Henceforward the main
objective of this work was to develop new TES materials with stabilized shape based
on inorganic salts (MgCl2middot6H2O MnCl2 and LiCl) and low-cost wastes from non-
metallic mining industry (bischofite and carnallite) by the sol-gel technique
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 757
previously developed with TEOS as monomer and via acid hydrolysis Thus the
influence of the chemical nature of the inorganic TES material was evaluated The
potential of the developed materials was analyzed for LHS and TCS
2 Materials and Procedures
21 Materials
Tetraethyl orthosilicate TEOS (reactant grade Sigma-Aldrich China) and
ethanol (absolute grade for analysis Merck Ka) were employed in the synthesis of
SiO2 materials as SMs The syntheses were produced by acid hydrolysis using
hydrochloric acid (37 ) of analysis grade obtained from Merck KGaA Germany
Magnesium chloride hexahydrate MgCl26H2O manganese chloride MnCl2 and
lithium chloride LiCl as reference material (all grade salts for analysis) were obtained
from Merck KGaA Germany Carnallite and bischofite were provided by the
Rockwood Lithium mining company Antofagasta Chile Distilled water was
obtained in the laboratory using a water deionizing system SIMS600CP MIlipore
Simplicity Personal Ultrapure Water System
22 Experimental procedure
The used sol-gel procedure was based on the method proposed by Milian et al
[23 24] via acid hydrolysis of the monomers to initiate the polymerization reaction
Briefly tetraethyl orthosilicate was mixed with the same amount of ethanol under
continuous stirring HCl (30 ) and distilled water were added and this solution was
continuously stirred over two hours to produce the -Si-O-Si- pre-polymer This pre-
polymeric solution was employed straight to develop the SS-TES materials The
selected inorganic materials (Table 1) previously dissolved in deionized water were
mixed with the prepolymer and then stored for 10 days Once the SS-TES materials
were achieved in solid phase materials were dried in an oven at 60 degC and finally
mechanically pulverized In this way sol-gel procedure was employed to obtain SS-
TES materials based on wastes from non-metallic mining industry bischofite
(MgCl2middot6H2O) and carnallite (KMgCl3middot6H2O) Eight new stabilized materials based
on bischofite and carnallite with different inorganic salt contents (Table 1) were
prepared
758middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
Table 1 Experimental conditions of cyclic stability studies for inorganic SS-
TES materials
Inorganic SS-TES materials
TES material content (wt )
Number of cycles
Temperature range (degC)
Coolingheating rate
LiCl 50 5 550 ndash 750
10 degC min-1
MgCl26H2O 50 2 30 ndash 150
MnCl2 50 2 25 ndash 200
Bischofite 20 30 40 and 60
2 25 ndash 150
Carnallite 20 30 40 and 60
2 25 ndash 150
23 SEM-EDX and XRD characterization of the SS-TES materials
The characterization of the new materials was performed by a Scanning Electron
Microscopy (SEM) with Energy Dispersion X-ray Spectroscopy (EDS) with a Jeol
machine Model JSM6360 LV a Siemens X-ray diffractometer (automatic and
computerized D5000 model) equipped with a scintillation detector and the
DiffracPlus software for X-ray diffraction (XRD) analysis
24 Thermal and cycling tests of the SS-TES materials
Thermal stability was studied using a thermogravimetry equipment (TG)
coupled with differential scanning calorimeter (DSC) (Mettler Toledo Model 1 1100
LF) from 100 to 350 degC with a heating cooling rate of 10 degC min-1 using around
10 mg of the sample and alumina crucible with lid Thermal properties like melting
temperature (Tm) and latent heat (ΔH) and cyclic stability of the obtained SS-PCM
were determined by a DSC 204 F1 Phoenix NETZSCH under a pure nitrogen
atmosphere with constant gas volumetric flow of 20 mL min-1 Cyclic stability was
determined by the DSC 204 F1 Phoenix NETZSCH using different temperature
ranges and cycle numbers for each sample (Table 1) to estabish the opportunities
of the developed SS-TES materials for LHS The same experiments specifically the
thermal dehydration processes of the hydrates were used to analyze the TCS
potentiality of the materials
3 Results and Discussion
Previously a sol-gel technique was developed to obtain SS-PCMs based on Li
salts [23] Now in this work the previously developed method was applied to obtain
SS-TES materials employing firstly inorganic salts and then wastes from the non-
metallic mining industry such as bischofite and carnallite The obtained SS-TES
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 759
materials were engaged not only for LHS but also for their potentiality as TCS
materials
31 Development of SS-TES materials employing commercial inorganic compounds
311 SEM-EDX and XRD characterization of SS-TES materials
Firstly 50 wt MgCl2middot6H2O and 50 wt MnCl2 were prepared by the
described method as two new SS-TES materials In addition a 50 wt LiCl based
material was also synthetized as a reference material of the sol-gel procedure
according to a previous publication [23] and to compare with new magnesium and
manganese based materials at the same salt content The SEM images obtained for
the MgCl2 based SS-TES material showed separated phases the SiO2 support
material with the saltand segregated salt particles which present an irregular
morphology and a flat surface respectively (Fig 1 a b and c) Smooth surface
particles were obtained for the MnCl2 stabilized material and the formation of
detached salt particles from the stabilized material was also observed (Fig 1 d e and
f) Conversely the LiCl salt was found covering the entire surface of the polymer as
well as forming part of the same solid phase of these particles (Fig 1 g h and I) as
was previously observed by Milian et al [23] The obtainment of separated phases by
this sol-gel technique was associated with a high weight percentage (wt) of the
TES material on the synthesis [23 24]
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 4
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 757
previously developed with TEOS as monomer and via acid hydrolysis Thus the
influence of the chemical nature of the inorganic TES material was evaluated The
potential of the developed materials was analyzed for LHS and TCS
2 Materials and Procedures
21 Materials
Tetraethyl orthosilicate TEOS (reactant grade Sigma-Aldrich China) and
ethanol (absolute grade for analysis Merck Ka) were employed in the synthesis of
SiO2 materials as SMs The syntheses were produced by acid hydrolysis using
hydrochloric acid (37 ) of analysis grade obtained from Merck KGaA Germany
Magnesium chloride hexahydrate MgCl26H2O manganese chloride MnCl2 and
lithium chloride LiCl as reference material (all grade salts for analysis) were obtained
from Merck KGaA Germany Carnallite and bischofite were provided by the
Rockwood Lithium mining company Antofagasta Chile Distilled water was
obtained in the laboratory using a water deionizing system SIMS600CP MIlipore
Simplicity Personal Ultrapure Water System
22 Experimental procedure
The used sol-gel procedure was based on the method proposed by Milian et al
[23 24] via acid hydrolysis of the monomers to initiate the polymerization reaction
Briefly tetraethyl orthosilicate was mixed with the same amount of ethanol under
continuous stirring HCl (30 ) and distilled water were added and this solution was
continuously stirred over two hours to produce the -Si-O-Si- pre-polymer This pre-
polymeric solution was employed straight to develop the SS-TES materials The
selected inorganic materials (Table 1) previously dissolved in deionized water were
mixed with the prepolymer and then stored for 10 days Once the SS-TES materials
were achieved in solid phase materials were dried in an oven at 60 degC and finally
mechanically pulverized In this way sol-gel procedure was employed to obtain SS-
TES materials based on wastes from non-metallic mining industry bischofite
(MgCl2middot6H2O) and carnallite (KMgCl3middot6H2O) Eight new stabilized materials based
on bischofite and carnallite with different inorganic salt contents (Table 1) were
prepared
758middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
Table 1 Experimental conditions of cyclic stability studies for inorganic SS-
TES materials
Inorganic SS-TES materials
TES material content (wt )
Number of cycles
Temperature range (degC)
Coolingheating rate
LiCl 50 5 550 ndash 750
10 degC min-1
MgCl26H2O 50 2 30 ndash 150
MnCl2 50 2 25 ndash 200
Bischofite 20 30 40 and 60
2 25 ndash 150
Carnallite 20 30 40 and 60
2 25 ndash 150
23 SEM-EDX and XRD characterization of the SS-TES materials
The characterization of the new materials was performed by a Scanning Electron
Microscopy (SEM) with Energy Dispersion X-ray Spectroscopy (EDS) with a Jeol
machine Model JSM6360 LV a Siemens X-ray diffractometer (automatic and
computerized D5000 model) equipped with a scintillation detector and the
DiffracPlus software for X-ray diffraction (XRD) analysis
24 Thermal and cycling tests of the SS-TES materials
Thermal stability was studied using a thermogravimetry equipment (TG)
coupled with differential scanning calorimeter (DSC) (Mettler Toledo Model 1 1100
LF) from 100 to 350 degC with a heating cooling rate of 10 degC min-1 using around
10 mg of the sample and alumina crucible with lid Thermal properties like melting
temperature (Tm) and latent heat (ΔH) and cyclic stability of the obtained SS-PCM
were determined by a DSC 204 F1 Phoenix NETZSCH under a pure nitrogen
atmosphere with constant gas volumetric flow of 20 mL min-1 Cyclic stability was
determined by the DSC 204 F1 Phoenix NETZSCH using different temperature
ranges and cycle numbers for each sample (Table 1) to estabish the opportunities
of the developed SS-TES materials for LHS The same experiments specifically the
thermal dehydration processes of the hydrates were used to analyze the TCS
potentiality of the materials
3 Results and Discussion
Previously a sol-gel technique was developed to obtain SS-PCMs based on Li
salts [23] Now in this work the previously developed method was applied to obtain
SS-TES materials employing firstly inorganic salts and then wastes from the non-
metallic mining industry such as bischofite and carnallite The obtained SS-TES
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 759
materials were engaged not only for LHS but also for their potentiality as TCS
materials
31 Development of SS-TES materials employing commercial inorganic compounds
311 SEM-EDX and XRD characterization of SS-TES materials
Firstly 50 wt MgCl2middot6H2O and 50 wt MnCl2 were prepared by the
described method as two new SS-TES materials In addition a 50 wt LiCl based
material was also synthetized as a reference material of the sol-gel procedure
according to a previous publication [23] and to compare with new magnesium and
manganese based materials at the same salt content The SEM images obtained for
the MgCl2 based SS-TES material showed separated phases the SiO2 support
material with the saltand segregated salt particles which present an irregular
morphology and a flat surface respectively (Fig 1 a b and c) Smooth surface
particles were obtained for the MnCl2 stabilized material and the formation of
detached salt particles from the stabilized material was also observed (Fig 1 d e and
f) Conversely the LiCl salt was found covering the entire surface of the polymer as
well as forming part of the same solid phase of these particles (Fig 1 g h and I) as
was previously observed by Milian et al [23] The obtainment of separated phases by
this sol-gel technique was associated with a high weight percentage (wt) of the
TES material on the synthesis [23 24]
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
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Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 5
758middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
Table 1 Experimental conditions of cyclic stability studies for inorganic SS-
TES materials
Inorganic SS-TES materials
TES material content (wt )
Number of cycles
Temperature range (degC)
Coolingheating rate
LiCl 50 5 550 ndash 750
10 degC min-1
MgCl26H2O 50 2 30 ndash 150
MnCl2 50 2 25 ndash 200
Bischofite 20 30 40 and 60
2 25 ndash 150
Carnallite 20 30 40 and 60
2 25 ndash 150
23 SEM-EDX and XRD characterization of the SS-TES materials
The characterization of the new materials was performed by a Scanning Electron
Microscopy (SEM) with Energy Dispersion X-ray Spectroscopy (EDS) with a Jeol
machine Model JSM6360 LV a Siemens X-ray diffractometer (automatic and
computerized D5000 model) equipped with a scintillation detector and the
DiffracPlus software for X-ray diffraction (XRD) analysis
24 Thermal and cycling tests of the SS-TES materials
Thermal stability was studied using a thermogravimetry equipment (TG)
coupled with differential scanning calorimeter (DSC) (Mettler Toledo Model 1 1100
LF) from 100 to 350 degC with a heating cooling rate of 10 degC min-1 using around
10 mg of the sample and alumina crucible with lid Thermal properties like melting
temperature (Tm) and latent heat (ΔH) and cyclic stability of the obtained SS-PCM
were determined by a DSC 204 F1 Phoenix NETZSCH under a pure nitrogen
atmosphere with constant gas volumetric flow of 20 mL min-1 Cyclic stability was
determined by the DSC 204 F1 Phoenix NETZSCH using different temperature
ranges and cycle numbers for each sample (Table 1) to estabish the opportunities
of the developed SS-TES materials for LHS The same experiments specifically the
thermal dehydration processes of the hydrates were used to analyze the TCS
potentiality of the materials
3 Results and Discussion
Previously a sol-gel technique was developed to obtain SS-PCMs based on Li
salts [23] Now in this work the previously developed method was applied to obtain
SS-TES materials employing firstly inorganic salts and then wastes from the non-
metallic mining industry such as bischofite and carnallite The obtained SS-TES
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 759
materials were engaged not only for LHS but also for their potentiality as TCS
materials
31 Development of SS-TES materials employing commercial inorganic compounds
311 SEM-EDX and XRD characterization of SS-TES materials
Firstly 50 wt MgCl2middot6H2O and 50 wt MnCl2 were prepared by the
described method as two new SS-TES materials In addition a 50 wt LiCl based
material was also synthetized as a reference material of the sol-gel procedure
according to a previous publication [23] and to compare with new magnesium and
manganese based materials at the same salt content The SEM images obtained for
the MgCl2 based SS-TES material showed separated phases the SiO2 support
material with the saltand segregated salt particles which present an irregular
morphology and a flat surface respectively (Fig 1 a b and c) Smooth surface
particles were obtained for the MnCl2 stabilized material and the formation of
detached salt particles from the stabilized material was also observed (Fig 1 d e and
f) Conversely the LiCl salt was found covering the entire surface of the polymer as
well as forming part of the same solid phase of these particles (Fig 1 g h and I) as
was previously observed by Milian et al [23] The obtainment of separated phases by
this sol-gel technique was associated with a high weight percentage (wt) of the
TES material on the synthesis [23 24]
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 6
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 759
materials were engaged not only for LHS but also for their potentiality as TCS
materials
31 Development of SS-TES materials employing commercial inorganic compounds
311 SEM-EDX and XRD characterization of SS-TES materials
Firstly 50 wt MgCl2middot6H2O and 50 wt MnCl2 were prepared by the
described method as two new SS-TES materials In addition a 50 wt LiCl based
material was also synthetized as a reference material of the sol-gel procedure
according to a previous publication [23] and to compare with new magnesium and
manganese based materials at the same salt content The SEM images obtained for
the MgCl2 based SS-TES material showed separated phases the SiO2 support
material with the saltand segregated salt particles which present an irregular
morphology and a flat surface respectively (Fig 1 a b and c) Smooth surface
particles were obtained for the MnCl2 stabilized material and the formation of
detached salt particles from the stabilized material was also observed (Fig 1 d e and
f) Conversely the LiCl salt was found covering the entire surface of the polymer as
well as forming part of the same solid phase of these particles (Fig 1 g h and I) as
was previously observed by Milian et al [23] The obtainment of separated phases by
this sol-gel technique was associated with a high weight percentage (wt) of the
TES material on the synthesis [23 24]
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 7
760middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
SEM images of SS-TES materials at 50 wt MgCl2 MnCl2 and LiCl
(a d and g respectively) and EDS micrographs (b and c e and f h and I
respectively)
312 Thermal and cycling performance of the SS-PCMs
The results of the thermal characterization of the synthesized compounds are
summarized in Table 2 For LHS it can be established that the LiCl SS-TES material
melts and crystallizes at 6078 and 6009 degC respectively presenting a storage heat
ΔHm of 1887 kJkg-1 (Table 2) while its latent interval RL was close to 2 degC
comparable with previous work [23] The manganese and magnesium chloride salts
did not show a typical PCM behavior since no solidification occurred MnCl2 SS-TES
material melts and degrades at the same temperature subsequently there was no
solidification process that allows the reuse of the stored energy while the SS-TES
material of MgCl26H2O lost its water molecules consequently there was no fusion
at low temperature or in the analyzed range (25 ndash 200 degC)
Table 2 Thermal properties of inorganic SS-TES materials prepared with
50 wt of TES material
SS-TES material Tm (degC) Ts (degC) ΔHm (kJ kg-1) ΔHs (kJ kg-1) RL
LiCl-SiO2 6009 6078 18872 1579 19
MgCl2-SiO2 - - - - -
MnCl2-SiO2 7011355 - 1053135027 - -
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 8
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 761
Based on the results it was concluded that the method applied to Mg or Mn
chlorides under the experimental conditions of this work did not developed SS-TES
materials suitable for LHS demonstrating that the success of the synthesis also
depends on the nature of the PCM Therefore it was decided to carry out a deeper
study with salts of industrial and mining interest bischofite and carnallite as cases of
study
32 Application of the sol-gel method to wastes from non-metallic mining industry
The use of by-products obtained from mining industry as TES materials is of
great interest due to its availability and continuous accumulation mainly in northern
Chile Further benefits are that wastes from mining industries presented low costs
and that their use decreases the environmental pollution caused by this sort of
activity The potential of bischofite and carnallite as TES materials has been evaluated
by the Thermal Energy Storage research group of Center for Advanced Research
in Lithium and Industrial Minerals (CELiMIN) [5 18]
Adittionally the thermal process of the bischofite was presented according to
the following decomposition reactions [10]
MgCl26H2O(s) MgCl24H2O(s) + 2H2O(g)
MgCl24H2O(s) MgCl22H2O(s) + 2H2O(g)
MgCl22H2O(s) MgCl2H2O(s) + H2O(g)
MgCl22H2O(s) MgOHCl(s) + H2O(g) +HCl(g)
Meanwhile carnallite was decomposed according to the following global
reaction between 100 and 400 degC [26]
KMgCl36H2O KCl + MgO + 5H2O + 2HCl
In our work the carnallite and bischofite samples were analyzed by TG-DSC to
have a reference of their thermal behaviour (Fig 2) after their stabilization by SiO2
Both samples started decomposition processes at low temperatures close to 100 degC
Then the sol-gel method was applied to obtain the SS-TES materials of these wastes
in order to improve their thermal properties mainly the thermal stability in search
of a possible application in TES systems
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 9
762middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
TG-DSC curve for bischofite (a) and carnallite (b)
321 SEM-EDX and XRD characterization of SS-TES materials
The XRD results for carnallite and bischofite SS-TES materials are presented in
Fig 3 The obtained patterns were compared with the XRD patterns of these
materials available in the PDF2 database The main peaks of bischofite were
observed for 60 wt bischofite material (Fig 3 a) therefore these analyzes allowed
to verify the recrystallization of this salt hydrate from synthesis solution Although
no diffraction signals were obtained for samples at lower amounts of bischofite (Fig
4 I b c d) due to the homogeneous dispersion of the salt hydrate into the silica SM
which is an amorphous material as was previously reported [2324] Nevertheless
main peaks of pure carnallite (Fig 3 b) were missing for carnallite SS-TES materials
(Fig 4 II) The absence of the main peaks of pure carnallite for carnallite SS-TES
materials indicated the presence of a different solid phase agglomerated in the surface
of the particles which was corroborated later with SEM-EDS analysis
On the one hand it was confirmed that bischofite remained stable during the
synthesis and in the final compound solidified as magnesium chloride hexahydrate
In addition the appearance of the main peaks for the SS-TES material with 60 wt
bischofite (2164 3390 3098 3276 2083 1531 2992 and 4941 deg2Ө ordered by
intensity) (Fig 4 IA) indicates the formation of bischofite agglomerations during the
synthesis at this weight percentage On the other hand the SS-TES materials of the
bischofite at lower salt hydrate contents did not show signals in the diffraction
patterns (Fig 4 b c d) indicating that the bischofite was homogeneously distributed
in the support material with no agglomerations
On the other hand peaks were obtained in the XRD pattern for all carnallite SS-
TES materials (Fig 4 II) except for the content of 20 wt This SS-TES compound
forms agglomerates at low percentages of the carnallite during synthesis attributed
to its lower solubility in the reaction medium when compared with bischofite
However the main peaks obtained for carnallite SS-TES materials (3771 2838
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 10
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 763
4543 and 6614 deg2Ө) do not correspond to the main signals corresponding to
carnallite database pattern (26 merit figure) (Fig 3) indicating a possible
dissociation dehydration and or non-agglomeration of an excess of the inorganic
salt after the condensation stage in the sol-gel process The XRD pattern of 60 wt
carnallite SS-TES material obtained in this work was compared with that obtained
in a study of carnallite dehydration at 400 degC [5] both patterns showed the same
signals (3771 2838 4543 and 6614 deg2Ө) The correspondence between these
patterns was further evidence of the dehydration of the carnallite [5] when exposed
to the sol-gel process
XRD patterns of a) 60 wt bischofite SS-TES material (above) and
the bischofite pattern available in PDF2 Database (below) b) 60 wt carnallite
SS-TES material (above) and carnallite available in PDF2 Database (below)
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 11
764middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
XRD patterns of bischofite (I) and carnallite (II) SS-TES materials at
different salt hydrate contents a) 60 wt b) 40 wt c) 30 wt and d) 20
wt
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 12
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 765
The samples were analyzed by SEM ndash EDS In the case of the bischofite SS-
TES materials a fairly homogeneous distribution of the salt and the polymer was
observed (Fig 5) which was found not only in the elemental analyzes by EDS (Fig
5 d e f) but it was also seen in the SEM image obtained with backscattered electrons
(Fig 5 b) where all the particles showed the same hue that is the same chemical
composition A combination of Mg and Si was observed so it was concluded that
the SiO2 polymer and the MgCl2 are in the same particles (Fig 5 c)
SEM micrographs of 60 wt bischofite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps obtained for Cl Mg and Si (d e f respectively) EDS element
composite map for Mg and Si (c)
SS-TES material of 60 wt carnallite (KMgCl36H2O) presented small particles
adhered to the surface of the stabilized particles (Fig 6 a) As can be observed
differences in composition appeared between these small particles and the stabilized
ones (Fig 6 b) The differences in composition were also confirmed thanks to the
EDS maps where Mg and K appear with greater intensity in different zones
indicating the segregation of carnallite into these cationic salts (Fig 6 d and e) As
well the EDS mapping corroborated the presence of separated phases since particles
with bright yellow can be distinguished which belong to K based material related to
the mentioned small particles (Fig 6 c) These results coincided with those obtained
by XRD (Fig 3 b) where the main peaks did not correspond to those present in the
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 13
766middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
KMgCl36H2O pattern but to the aggregated small particles on the surface of the
material
SEM micrographs of 60 wt carnallite SS-TES material a) obtained
by secondary electrons and b) by backscattered electrons In addition EDS
element maps for Mg K and Si (d e f respectively) EDS element composite
map of Mg and K (c)
A deeper analysis by EDS allowed to identify the different phases appearing on
the surface of the carnallite SS-TES material and the composition of the larger
particles of this material In this regard different EDS points analyzes were
performed (Fig 7) Point 1 corresponds to adhered particles that according to the
images by backscattered electrons have the same composition as the larger particle
(point 3) while point 2 corresponded to particles with visibly different composition
(Fig 7 a) Elemental analyzes showed that points 1 and 3 are composed by the SS-
TES material of KMgCl36H2O while point 2 corresponds to a mix of KCl and SiO2
mixture (Table 3) The partial dissociation of carnallite in potassium chloride
(according to atomic percentage showed in Table 2 and XRD patterns (Fig 4) was
attributed to the dissolution of the salt during the sol-gel process and its subsequent
separately recrystallization in its different components
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 14
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 767
SEM micrograph of the surface of a particle of 60 wt carnallite
SS-TES material with different particles (M5_1_1 and M5_1_2) adhered to the
surface (M5_1_3)
Table 3 Elemental analysis by EDS of SS-TES material particles with
carnallite (60 wt)
Point Element AN Normal C (wt) Atomic C (at)
(M5_1_1)
O 8 5821 7253
Si 14 2597 1843
Cl 17 953 536
K 19 426 217
Mg 12 120 099
S 16 084 052
Total 10000 10000
(M5_1_2)
K 19 4712 3425
O 8 2146 3812
Cl 17 1983 1590
Si 14 1159 1173
Total 10000 10000
(M5_1_3)
O 8 5300 6828
Si 14 2897 2126
Cl 17 886 515
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 15
768middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
K 19 747 394
Mg 12 138 117
S 16 031 020
Total 10000 10000
322 Thermal and cycling performance of the SS-PCMs
Once more when thermal results were analyzed the presence of the bischofite
can be confirmed in the SS-TES materials by TG-DSC (Fig 8 I) However
improvements in the thermal properties of bischofite-based materials were not
achieved (Fig 8) for LHS since the process of heat store during phase change arose
simultaneously with hydrate degradation (weight loss occurred) At the same time
the heat involved in the thermal dehydration process of these materials increases
with the increase in the amount of the hydrate added to the synthesis (Fig 8 a b
c)
TG-DSC curve for SS-TES materials obtained with bischofite (I) and
carnallite (II) and different amounts of TES material 30 40 and 60 wt (a b
and c respectively)
Cooling heating studies were performed for these samples but solidification
process of the materials does not occur for any of the two salt hydrates In addition
both SS-TES materials exhibit the same thermal degradation behavior as the pure
salts indicating that the used method did not influence or improve the heat storing
process Furthermore bischofite does not undergo complete dehydration after the
sol-gel synthesis process as in the case of previous work with Na2SO410H2O salt
[24]
Finally a single peak at 50 degC along with an increase in the mass of the material
was observed for carnallite SS-TES material (Fig 8 II) which may indicate water
absorption by the carnallite alike other reported works [9] The peak at 50 degC in the
carnallite samples was stabilized by the SiO2 particles (Fig 8 II) being much higher
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 16
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 769
than that of non-stabilized carnallite (Fig 2 b) Water absorption process by
carnallite could be favored when the salt was stabilized by the sol-gel method In
other words the use of the applied sol-gel method results in the stabilization of
carnallite displaying a possible high potential for applications in storage of
thermochemical energy (TCS) which most be further analyzed Recently similar
works have been published which propose SS-TES materials for TCS and based on
SiO2 as SMs CaCl2 salt was stabilized in vermiculite employing a laboratory scale
reactor (127 cm3) with a scaled maximum power density around 150 kW m-3 [27]
Likewise a new SS-TES material was developed by impregnation method for low-
grade TCS based on silica gel as SM and 30 wt of MgSO4middot7H2O Al2(SO4)3middot18H2O
and CuSO4middot5H2O with high storage density values of 7927 5805 and 7126 J g-1
respectively [28] As a result further works could be directed to analyze the
performance of the carnallite-SiO2 based SS-TES material and the operating settings
like partial pressure temperature range the chemical reversibility dehydration and
hydration isotherms and energy storage density similar to the work published
recently by Mamani and coworkers [29]
4 Conclusions
A one-step method based on a sol-gel process was applied to obtain SS-TES
materials of commercial MgCl26H2O MnCl2 LiCl and wastes from non-metallic
mining industry bischofite and carnallite SEM analysis allowed to determine the
morphology of samples and to analyze the achievement of shape stabilization of the
TES materials According to the TG-DSC performances it was concluded that
MgCl2 and MnCl2 based SS-TES materials did not crystalized so no heat storage
occurs under the experimental conditions therefore demonstrating that
improvement of thermal properties by this sol-gel method for shape-stabilized
materials also depends on the nature of the inorganic compound
New stabilized materials based on bischofite and carnalite were obtained
through the direct sol-gel process using TEOS as monomer and via acid hydrolysis
However the cooling heating studies allowed to prove that the solidification
process of the SS-TES materials did not occur which demonstrates the relevance of
the chemical and thermal nature of the inorganic salt selected as TES material
Moreover SS-TES materials exhibited the same thermal degradation behavior as the
pure salts which means that SiO2 as support material did not influence this thermal
process Therefore the employed sol-gel technique did not improve the thermal
properties of these materials for LHS using MgCl2 MnCl2 bischofite or carnallite as
occurs for LiCl Conversely the new material of carnallite SiO2 showed a water
absortion peak stabilized and enhanced by the presence of the SiO2 support material
which could indicate a high potential as a thermochemical storage medium However
further studies related to the recovery of the stored heat by this carnallite ndash silica TES
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 17
770middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
materials should be performed in order to analyze it availability for TES applications
like the recycle of industrial waste heat or seasonal thermochemical storage
applications
Funding
The work was partially funded by the Chilean government ANIDFONDAP
No 15110019 CONICYTFONDECYT REGULAR Ndeg1170675
CONICYTPCIREDES Ndeg 170131 CONICYTBECA DE DOCTORADO
NACIONAL 2015 Ndeg21150240 CORFO 16ENI2-71940 INGENIERIA2030
projects and ANIDFONDECYT DE POSTDOCTORADO 2020 Nordm 3200786
References
[1] Alva G Lin Y Fang G (2018) An overview of thermal energy storage
systems Energy 144341-378
[2] Scapino L De Servi C Zondag HA Diriken J Rindt CC Sciacovelli A
(2020) Techno-economic optimization of an energy system with sorption
thermal energy storage in different energy markets Appl Energy 258114063
[3] Mohamed SA Al-Sulaiman FA Ibrahim NI Zahir MH Al-Ahmed A Saidur
R Sahin AZ (2017) A review on current status and challenges of inorganic
phase change materials for thermal energy storage systems Renewable
Sustainable Energy Rev 701072-1089
[4] Gutierrez A Miroacute L Gil A Rodriacuteguez-Aseguinolaza J Barreneche C Calvet
N Cabeza LF (2016) Advances in the valorization of waste and by-product
materials as thermal energy storage (TES) materials Renewable Sustainable
Energy Rev 59763-783
[5] Gutierrez A Ushak S Mamani V Vargas P Barreneche C Cabeza LF
Graacutegeda M (2017) Characterization of wastes based on inorganic double salt
hydrates as potential thermal energy storage materials Sol Energy Mater Sol
Cells 170149ndash59
[6] Ushak S Gutierrez A Flores E Galleguillos H Grageda M (2014)
Development of thermal energy storage materials from waste-process salts
Energy Procedia 57(0)627-632 doi 101016jegypro201410217
[7] Miroacute L Navarro ME Suresh P Gil A Fernaacutendez A I Cabeza LF (2014)
Experimental characterization of a solid industrial by-product as material for
high temperature sensible thermal energy storage (TES) Appl Energy
1131261-1268
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 18
ACTA NOVA Vol 9 Nordm 5 y 6 noviembre 2020 ISSN 1683-0768 Artiacuteculos Cientiacuteficos 771
[8] Gasia J Gutierrez A Peiroacute G Miroacute L Grageda M Ushak S Cabeza LF
(2015) Thermal performance evaluation of bischofite at pilot plant scale
Appl Energy 155826-833
[9] Gutierrez A Ushak S Linder M (2018) High Carnallite-Bearing Material for
Thermochemical Energy Storage Thermophysical Characterization ACS
Sustainable Chem Eng 6(5)6135-6145
[10] Mamani V Gutieacuterrez A Ushak S (2018) Development of low-cost inorganic
salt hydrate as a thermochemical energy storage material Sol Energy Mater
Sol Cells 176346-356
[11] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738
[12] Ushak S Gutierrez A Galleguillos H Fernandez AG Cabeza LF Graacutegeda M
(2015) Solar Energy Materials amp Solar Cells Thermophysical characterization
of a by-product from the non-metallic industry as inorganic PCM Sol Energy
Mater Sol Cells 132385ndash91
[13] Galazutdinova Y Al‐Hallaj S Graacutegeda M Ushak S (2020) Development of
the inorganic composite phase change materials for passive thermal
management of Li‐ion batteries material characterization Int J Energy Res
44(3)2011-2022
[14] Miliaacuten YE Gutieacuterrez A Graacutegeda M Ushak S (2017) A review on
encapsulation techniques for inorganic phase change materials and the
influence on their thermophysical properties Renew Sustain Energy Rev
73983ndash99
[15] Giro-paloma J Martiacutenez M Cabeza LF Fernaacutendez AI (2016) Types
methods techniques and applications for microencapsulated phase change
materials (MPCM) A review Renew Sustain Energy Rev 531059ndash75
[16] Safari A Saidur R Sulaiman FA Xu Y Dong J (2017) A review on
supercooling of Phase Change Materials in thermal energy storage systems
Renew Sustain Energy Rev 70905ndash19
[17] Galazutdinova Y Graacutegeda M Cabeza LF Ushak S (2017) Novel inorganic
binary mixture for low‐temperature heat storage applications Int J Energy
Res 41(14)2356-2364
[18] Ushak S Cruz MJ Cabeza LF Graacutegeda M (2016) Preparation and
characterization of inorganic PCM microcapsules by fluidized bed method
Materials 9(1)24 httpsdoiorg103390ma9010024
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738
Page 19
772middot Milian Y amp Ushak S Development of shape stabilized thermal energy storage
[19] Ling Z Liu J Wang Q Lin W Fang X Zhang Z (2017) MgCl2middot6H2O-
Mg(NO3)2middot6H2O eutecticSiO2composite phase change material with
improved thermal reliability and enhanced thermal conductivity Sol Energy
Mater Sol Cells 172195ndash201
[20] Fan S Gao H Dong W Tang J Wang J Yang M Wang G (2017) Shape‐
stabilized phase change materials based on stearic acid and mesoporous
hollow SiO2 microspheres (SASiO2) for thermal energy storage Eur J Inorg
Chem 142138-2143
[21] Wang CL Yeh KL Chen CW Lee Y Lee HL Lee T (2017) A quick-fix
design of phase change material by particle blending and spherical
agglomeration Appl Energy 191239ndash50
[22] Wu Y Wang T (2014) Preparation and characterization of hydrated salts
silica composite as shape-stabilized phase change material via sol ndash gel
process Thermochim Acta 201459110ndash5
[23] Miliaacuten YE Reinaga N Graacutegeda M Ushak S (2020) Development of new
inorganic shape stabilized phase change materials with LiNO3 and LiCl salts
by sol-gel method J Sol-Gel Sci Technol 9422ndash33
[24] Milian YE Ushak S (2020) Design of synthesis route for inorganic shape-
stabilized phase change materials Direct solndashgel process versus vacuum
impregnation method J Sol-Gel Sci Technol 9467ndash79
[25] Xu Z Yuan Z Zhang D Chen W Huang Y Zhang T Sun Z (2018) Highly
mesoporous activated carbon synthesized by pyrolysis of waste polyester
textiles and MgCl2 Physiochemical characteristics and pore-forming
mechanism J Cleaner Prod 192453-461
[26] Ashboren D (1973) Carnallite decomposition into magnesia hydrochloric
acid and potassium chloride A thermal analysis study formation of pure
periclase J Appl Chem Biotechnol 23(1)77-86
[27] Walsh S Reynolds J Abbas B Woods R Searle J Jewell E Elvins J (2020)
Assessing the Dynamic Performance of Thermochemical Storage Materials
Energies 13(9)2202 httpsdoiorg103390en13092202
[28] Ousaleh HA Said S Zaki A Faik A El Bouari A (2020) Silica gelinorganic
salts composites for thermochemical heat storage Improvement of energy
storage density and assessment of cycling stability Materials Today
Proceedings httpsdoiorg101016jmatpr202004354
[29] Mamani V Gutieacuterrez A Fernaacutendez AI Ushak S (2020) Industrial carnallite-
waste for thermochemical energy storage application Appl Energy
265114738 httpsdoiorg101016japenergy2020114738